What about the marriage gap?

The results are in, but the 2010 elections remain a mystery. That’s because a core, and ever expanding, constituency was ignored by politicians and pollsters. Until we understand what happened with unmarried women voters, we cannot know the deeper dynamics that shaped this election — or anticipate their consequences for 2012.

Unmarried women are a key part of the electorate, and their numbers are growing rapidly as the face of the American family changes. The number of unmarried Americans as a whole has risen dramatically, according to a recent Pew Research Center Social & Demographic Trends report. In 1960, close to three-quarters (72 percent) of adult Americans were married; today, about half (52 percent) are. One out of every two American women today is single, separated, divorced or widowed. It’s now 48.6 percent, up from just 30 percent in 1960.

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Unmarried women, along with young people and people of color, now make up 53 percent of the voting-eligible population. This new majority, the “rising American electorate,” is the fastest-growing large demographic group. In fact, according to the latest census data, the RAE accounted for 81 percent of the population growth between 2000 and 2010, and a jaw-dropping 95 percent between 2008 and 2010.

Unmarried women make up the fastest-growing group within the RAE. Yet they are still under-represented among voters. In 2010, the RAE was approximately 40 percent of all voters; in 2008, they represented 47 percent. However, their astounding growth rates ensure that they will be an ever-increasing share of U.S. voters.

These demographic shifts have major, but largely unacknowledged, political implications. This midterm, the political analysts still focused on the gender gap. Exit pollsters did not even include marital status as one of their key questions.

But in 2010, it was again marital status, and especially the marriage gap — the difference between how unmarried and married women register and vote — that proved far more determinative than the gender gap.

Married women are far more likely to register and vote than unmarried women; and unmarried women are remarkably different in their preference for candidates. This holds true across all demographic groups — including age, race and education. In 2010, according to Greenberg Quinlan Rosner Research, the marriage gap was 30 points — more than double the 13-point gender gap.

The marriage gap and unmarried women are key factors in electoral outcomes. In 2004, unmarried women voted for Democratic Sen. John Kerry over President George W. Bush by 62 percent to 37 percent. In 2008, unmarried women voted for Barack Obama over Sen. John McCain, 70 percent to 29 percent.

And in 2010, the marriage gap held in races around the country. The latest polling data again show how critical unmarried women were, and likely will continue to be, in close races: